为了实现这一目标，您可以尝试覆盖相关方法，就像下面显示的代码一样。

In order to achieve this goal, you can try to override related methods, just like code shown as follows.

    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            menuStrip1.Renderer = new MenuItemRenderer();
        }
        private void item1ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            MessageBox.Show("click item1");
        }    
    }

    class MenuBarColor : ProfessionalColorTable
    {
        // mainmenutirp bg color
        Color ManuBarCommonColor = Color.Transparent;
        // all items border
        Color MenuBorderColor = Color.Black;
        // mianmenutrip border
        Color MenuItemBorderColor = Color.Transparent;
        public MenuBarColor()
        {
        }
        #region
        public override Color MenuItemPressedGradientBegin
        {
            get
            {
                return ManuBarCommonColor;
            }
        }
        public override Color MenuItemPressedGradientEnd
        {
            get
            {
                return ManuBarCommonColor;
            }
        }
        public override Color MenuItemPressedGradientMiddle
        {
            get
            {
                return ManuBarCommonColor;
            }
        }
        public override Color ButtonSelectedHighlight
        {
            get
            {
                return ManuBarCommonColor;
            }
        }
        public override Color MenuItemSelectedGradientBegin
        {
            get
            {
                return ManuBarCommonColor;
            }
        }
        public override Color MenuItemSelectedGradientEnd
        {
            get
            {
                return ManuBarCommonColor;
            }
        }
        public override Color MenuBorder
        {
            get
            {
                return MenuBorderColor;
            }
        }
        public override Color MenuItemBorder
        {
            get
            {
                return MenuItemBorderColor;
            }
        }
        #endregion
    }
    class MenuItemRenderer : ToolStripProfessionalRenderer
    {
        // text
        Font textFont = new System.Drawing.Font("Arial", 9F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(0)));
        private Color menuItemSelectedColor = Color.Black;
        private Color menuItemBorderColor = Color.Red;
        public MenuItemRenderer() : base(new MenuBarColor())
        {
            // item bg color
            this.menuItemSelectedColor = Color.Transparent;
            // item border
            this.menuItemBorderColor = Color.Transparent;
        }
        protected override void OnRenderItemText(ToolStripItemTextRenderEventArgs e)
        {
            e.TextFont = textFont;
            if (e.Item.IsOnDropDown)
            {
                e.TextColor = Color.Black;
            }
            base.OnRenderItemText(e);
        }

        protected override void OnRenderMenuItemBackground(ToolStripItemRenderEventArgs e)
        {
            if (e.Item.IsOnDropDown)
            {
                if (e.Item.Selected == true && e.Item.Enabled)
                {
                    DrawMenuDropDownItemHighlight(e);
                }
            }
            else
            {
                base.OnRenderMenuItemBackground(e);
            }
        }

        private void DrawMenuDropDownItemHighlight(ToolStripItemRenderEventArgs e)
        {
            Rectangle rect = new Rectangle();
            rect = new Rectangle(2, 0, (int)e.Graphics.VisibleClipBounds.Width - 4, (int)e.Graphics.VisibleClipBounds.Height - 1);
            using (SolidBrush brush = new SolidBrush(menuItemSelectedColor))
            {
                e.Graphics.FillRectangle(brush, rect);
            }
            using (Pen pen = new Pen(menuItemBorderColor))
            {
                e.Graphics.DrawRectangle(pen, rect);
            }
        }
    }

问候，

Stanly